Which characteristic laboratory test helps identify Vibrio species in stool and what is the typical selective medium?

Which characteristic laboratory test helps identify Vibrio species in stool and what is the typical selective medium?

• A. Oxidase-positive curved Gram-negative rods; TCBS agar
• B. Gram-positive rods; blood agar
• C. Acid-fast bacilli; Lowenstein-Jensen medium
• D. Catalase-positive cocci; mannitol salt agar

Answer: (A)

Vibrio in stool is best recognized by its oxidase-positive reaction and its curved, Gram-negative rod appearance, and then confirmed by using a selective, differential medium that highlights Vibrio growth. The oxidase test helps separate vibrios from many other Gram-negative rods, since vibrios are typically oxidase positive. The curved rod shape seen under the microscope further nudges you toward Vibrio rather than straight-rod enterics. For culture, the classic selective medium is TCBS agar (thiosulfate-citrate-bile salts-sucrose). The bile salts and alkaline pH suppress many other bacteria, allowing Vibrio to grow, and the sucrose differential lets you distinguish species: Vibrio cholerae usually makes yellow colonies due to sucrose fermentation, while other vibrios may form green colonies. This combination of a positive oxidase reaction, curved Gram-negative rods, and growth with characteristic colony colors on TCBS is the best approach to identify Vibrio in stool. Other options point to organisms not associated with Vibrio—for example, Gram-positive rods on blood agar, acid-fast bacilli on a specialized medium, or catalase-positive cocci on mannitol salt agar.

Vibrio in stool is best recognized by its oxidase-positive reaction and its curved, Gram-negative rod appearance, and then confirmed by using a selective, differential medium that highlights Vibrio growth. The oxidase test helps separate vibrios from many other Gram-negative rods, since vibrios are typically oxidase positive. The curved rod shape seen under the microscope further nudges you toward Vibrio rather than straight-rod enterics.

For culture, the classic selective medium is TCBS agar (thiosulfate-citrate-bile salts-sucrose). The bile salts and alkaline pH suppress many other bacteria, allowing Vibrio to grow, and the sucrose differential lets you distinguish species: Vibrio cholerae usually makes yellow colonies due to sucrose fermentation, while other vibrios may form green colonies. This combination of a positive oxidase reaction, curved Gram-negative rods, and growth with characteristic colony colors on TCBS is the best approach to identify Vibrio in stool.

Other options point to organisms not associated with Vibrio—for example, Gram-positive rods on blood agar, acid-fast bacilli on a specialized medium, or catalase-positive cocci on mannitol salt agar.